In a conventional circuit board used as a circuit board for a large current, a metal circuit plate shaped like a circuit pattern to receive a large current, insulating substrates made of a ceramic material, a metallic heat diffusing plate used as a means for spreading heat from an electronic component, such as a power module, mounted on the metal circuit plate in the lateral direction, and a metallic heat dissipating plate used for heat dissipation are stacked in this order and are bonded together with a brazing material (see, for example, PTL 1).